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Saturday, June 23, 2012

Making of a Field Coil Speaker, Part 4: LV FC PSU


Finally I found some time to continue with the work on the speaker system. Up to now the woofer field coils were powered form an ordinary lab power supply. This got replaced now by something more appropriate.

A dedicated power supply for the woofers in a similar style as the high voltage field coil supply  of the horn drivers. The woofers are running at 7-9V / 3A. So no tube rectification. The PSU provides two independant voltages for the left and right woofers. Schottky diodes are used for the rectification. The filter is choke input using Lundahl LL2733 filament chokes.

As power transformers two of my 5A filament transformers are used for each side. Since each transformer only delivers up to 10V when all secondaries are wired in series, two of them needed to be cascaded to reach the desired output voltage range.

The supply is configurable with switches to adjust output voltage. The filter can be selected between pure choke input, or cap input with two different capacitance values:

Some pics of the assembly process, power transformers and some caps mounted:

Some wiring:

The completed supply before the bottom lid is attached:

The chokes provide a well filtered low noise output voltage. Smoother and more delicate sound compared to the ordinary lab supply!

Both the high voltage horn driver supply and the  new one besides each other:

The voltage indicators are still missing on the new one, these will be added later.

Next the system will get a crossover in the same style as the one I built for Twogoodear's Gotorama system. Stay tuned!

Best regards



  1. hi. can you post shematics of you FC power supply,? how it comapares to battery ?

    1. Hi! I provide the schematics when the parts for the supply are bought from me. I never tried a battery supply as out would be too tedious for such kind of currents. Everybody who uses my FC yuppie is happy with them

    2. how much cost supply for supravox 215-2000EXC fielcoils? i intend to use at 12V , current would be about 3.5-5A

    3. for pricing please contact me by email. You need to provide exact current specifications, 3.5-5A is not specific enough